The present disclosure relates to image forming apparatuses for use in copiers, printers, facsimile machines, multifunction products, that is, products having the functions of the just-mentioned devices integrated together, etc., and more particularly relates to image forming apparatuses in which a toner image on an image carrying member is transferred to a recording medium carried on a transport belt, or to an intermediary transfer belt.
There are conventionally known image forming apparatuses in which a recording medium carried on a transport belt is transported and, at a nip portion formed between the transport belt and an image carrying member, a toner image formed on the image carrying member is transferred to the recording medium. When the toner image on the image carrying member is transferred to the recording medium on the transport belt, a transferring member such as a transfer roller makes contact with the inner circumferential surface of the transport belt, and a voltage applied to the transferring member causes electric charge to be applied, via the transport belt, to the recording medium. This causes the toner image to be transferred to the recording medium.
Inconveniently, in the upstream-side vicinity of the nip portion with respect to the movement direction of the transport belt, a gap may be produced between the transport belt and the image carrying member. Then, immediately before the toner image on the image carrying member is transferred to the recording medium, electric discharge occurs between the transport belt and the image carrying member. This abnormal electric discharge disturbs the toner image on the image carrying member, resulting in poor image quality.
Thus, there are known related technologies for preventing abnormal electric discharge as mentioned above. For example, there is known an image forming apparatus in which a transport belt is deformed so as to make contact with and adhere closely to an image carrying member. In this image forming apparatus, on the upstream side of the nip portion, a plate-form lifting member is arranged. The lifting member lifts up the transport belt toward the image carrying member. This eliminates a gap in the upstream-side vicinity of the nip portion and thereby prevents abnormal electric discharge.
However, while abnormal electric discharge in a region near the nip portion before transfer is prevented, abnormal electric discharge also occurs in a width-direction end part of the transport belt. When a width-direction end part of the transport belt sags down between a driving roller and a following roller, the end part hangs down. This produces a gap, in an end part in the vicinity of the nip portion, between the transport belt and the image carrying member.
Also, the shafts of the driving roller and the following roller across which the transport belt is laid may be fitted with an inclination relative to each other. In that case, the transport belt moves with an inclination, and one width-direction end part of the transport belt makes contact with the image carrying member. An opposite end part, however, comes apart from the image carrying member, and a gap is produced between the transport belt and the image carrying member.
In this gap in the end part, from a transferring member to which a voltage is applied, electric charge is discharged to the image carrying member. Moreover, the electric charge accumulated on the transport belt is discharged to the image carrying member, and this may destroy the photosensitive layer on the image carrying member. The above-mentioned abnormal electric discharge in an end part of an image carrying member can occur also in an image forming apparatus in which a toner image formed on an image carrying member is transferred to an intermediary transfer belt.
Made with a view to overcoming the inconveniences discussed above, the present disclosure aims to provide an image forming apparatus that suppresses abnormal electric discharge in a width-direction end part of a transport belt or an intermediary transfer belt during transfer of a toner image formed on an image carrying member to a recording medium on the transport belt or to the intermediary transfer belt.